Commercial hybrid restorative composite such as Z100®(3M) and Tetric® Ceram(Vivadent) has been prepared by mixing organic polymer and inorganic fillers. Z100® for instance contains ZrO2 and SiO2 inorganic fillers of which the total content is 79% wt). The particle size is between 0.01 and 3.5 μm. The monomer matrix comprises Bis-phenol-A glycidoxymethacrylates (Bis-GMA) and triethyleneglycoldimethacrylate (TEGDMA). Bis-GMA is the primary organic ingredient in nearly every commercial restorative resin. U.S. Pat. No. 3,066,112 to R. F. Bowen discloses a method of the synthesis of Bis-GMA, a monomer with two methacrylate functional groups and molecular weight about 512, from diglycidyl ether of bisphenol A (DGEBA) and methacrylic acid. Though the composite based on Bis-GMA has become major material for dental restoration due to its superior aesthetic quality, simple operation technique and enhanced mechanical strength, there are still problems. Volumetric shrinkage ranging from 2.6% to 7.1% after curing causes microleakage, a well-known effect of contraction gaps on the interface of resin and tooth. Saliva, fluid, food residue and microorganism trapped in the gaps lead to decayed tooth and damaged material, which is the major problem in nowadays restorative and esthetic dentistry. Therefore it is our object to provide a material with satisfactory mechanical properties and low polymerization shrinkage.
Joachim in Pat. No. WO 98/36279 discloses the use of highly branched methacrylate macro monomer, of which the molecular weight is from 2000 to 25000 g/mol, as the polymerizable resin. The high molecular weight polymerizable resin has fewer functional groups than that of low molecular weight monomer. The curing contraction is due to the reduction of free volume obtained from polymerization of functional groups. Therefore, the contraction can be reduced using high molecular weight monomer. However increasing molecular weight of monomers is combined with an increasing viscosity of the monomer and this makes it difficult to apply in clinic. Bowman in U.S. Pat. No. 5,730,601 discloses the use of mixing poly(ethylene glycol)dimethacrylate (PEGDMA) of which the molecular weight is from 600-800 g/mol and Bis-GMA as organic monomers. The long chain lowers the number of functional groups in molecule. However the poly(ethylene glycol) structure can easily twist and plasticize the cured resin to reduce their mechanical strength. The polymerization shrinkage consequently cannot be effectively reduced if monomers with methacrylate functional groups were used. A need exists therefore, for a resin monomer with less curing contraction to replace those with methacrylate groups as monomer sources. The object of the invention Is to provide a material with satisfactory mechanical properties, convenient operational techniques and respectively low polymerization shrinkage.